Conventionally, in a junction area between two waveguides, for example between a rib waveguide and a strip waveguide, the slab of the rib waveguide is gradually reduced until it is the same width as the rib of the strip waveguide.
As illustrated in FIGS. 1 and 2, this type of junction may conventionally be produced via a first operation of partially etching a silicon film 1, which etching operation is achieved using a first mask M1 (FIG. 1) and allows a first region 2, delimiting the slab and the rib of the rib waveguide, and in particular the portion of the slab of the first waveguide whose width gradually decreases, to be etched.
A second etching operation, achieved using a second mask M2 (FIG. 2), allows the strip waveguide to be delimited and a region 3 of the insulating layer located on either side of the two waveguides to be completely etched.
However, while carrying out the two etching operations, it is possible for alignment errors to occur between the two masks, for example an offset along the transverse axis X that may potentially exceed 30 nanometers.
For strip waveguides of conventional widths, for example, of a few hundred nanometers, these offsets lead to discontinuities, or walls, at the junction between the two waveguides, causing substantial attenuations of the optical signal or parasitic reflections.